US10372283B2 - Electronic device - Google Patents

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US10372283B2
US10372283B2 US15/872,980 US201815872980A US10372283B2 US 10372283 B2 US10372283 B2 US 10372283B2 US 201815872980 A US201815872980 A US 201815872980A US 10372283 B2 US10372283 B2 US 10372283B2
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capacitor
coupled
terminal
capacitors
electronic device
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US20180203544A1 (en
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Thomas Suwald
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NXP BV
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F21/00—Security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
    • G06F21/70—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer
    • G06F21/71—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer to assure secure computing or processing of information
    • G06F21/77—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer to assure secure computing or processing of information in smart cards
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/044—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by capacitive means
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/0416—Control or interface arrangements specially adapted for digitisers
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/0416—Control or interface arrangements specially adapted for digitisers
    • G06F3/04166—Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/0723—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/073—Special arrangements for circuits, e.g. for protecting identification code in memory
    • G06K19/07309—Means for preventing undesired reading or writing from or onto record carriers
    • G06K19/07345—Means for preventing undesired reading or writing from or onto record carriers by activating or deactivating at least a part of the circuit on the record carrier, e.g. ON/OFF switches
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
    • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
    • H03K17/96—Touch switches
    • H03K17/962—Capacitive touch switches
    • H03K17/9622—Capacitive touch switches using a plurality of detectors, e.g. keyboard
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2203/00—Indexing scheme relating to G06F3/00 - G06F3/048
    • G06F2203/041—Indexing scheme relating to G06F3/041 - G06F3/045
    • G06F2203/04103—Manufacturing, i.e. details related to manufacturing processes specially suited for touch sensitive devices
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C27/00—Electric analogue stores, e.g. for storing instantaneous values
    • G11C27/02—Sample-and-hold arrangements
    • G11C27/024—Sample-and-hold arrangements using a capacitive memory element
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K2217/00—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00
    • H03K2217/94—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated
    • H03K2217/96—Touch switches
    • H03K2217/9607—Capacitive touch switches
    • H03K2217/960735—Capacitive touch switches characterised by circuit details
    • H03K2217/96074—Switched capacitor

Definitions

  • the present disclosure relates to an electronic device for use in a touch-based user interface. Furthermore, the present disclosure relates to a corresponding method of manufacturing an electronic device.
  • smart cards may be used as electronic identity (eID) cards and payment cards bank cards).
  • eID electronic identity
  • payment cards bank cards are usually not equipped with a user interface suitable for entering user credentials, i.e. a so-called “authentication interface”.
  • authentication interface a so-called “authentication interface”.
  • Some smart cards have been equipped with embedded touch-based user interfaces, such as capacitive sensor structures. However, it may be difficult to implement a touch-based interface that accurately captures touch events while using only a small amount of power.
  • an electronic device for use in a touch-based user interface comprising a first capacitor, a second capacitor, a third capacitor, and an analog-to-digital converter, wherein: the first capacitor and the second capacitor are switchably coupled to each other; the first capacitor is switchably coupled to an input of the analog-to-digital converter; the second capacitor is coupled to the input of the analog-to-digital converter; the third capacitor is coupled to the first capacitor; the third capacitor is switchably coupled to the second capacitor; the third capacitor is switchably coupled to the input of the analog-to-digital converter.
  • the third capacitor is implemented as a printed circuit board capacitor.
  • the electronic device comprises a set of first capacitors.
  • the electronic device is configured to derive individual capacitances on the first capacitors from partial sum values, wherein said partial sum values are obtained by measuring capacitances on subsets of the set of first capacitors. In one or more embodiments, the electronic device is further configured to measure capacitances on mutually different subsets of the set of first capacitors.
  • the electronic device is further configured to apply a weighting factor to the partial sum values.
  • the electronic device is further configured to regroup the weighted partial sum values, thereby yielding high-pass filter terms.
  • the electronic device is further configured to filter the partial sum values.
  • the electronic device is further configured to use an infinite-impulse-response filter for filtering the partial sum values.
  • the first capacitors are coupled to general-purpose input/output pins.
  • the general-purpose input/output pins, the analog-to-digital converter and the second capacitor form part of a microcontroller unit.
  • a smart card comprises an electronic device of the kind set forth.
  • a method of manufacturing an electronic device for use in a touch-based user interface comprising providing the electronic device with a first capacitor, a second capacitor, a third capacitor, and an analog-to-digital converter, wherein: the first capacitor and the second capacitor are switchably coupled to each other; the first capacitor is switchably coupled to an input of the analog-to-digital converter; the second capacitor is coupled to the input of the analog-to-digital converter; the third capacitor is coupled to the first capacitor; the third capacitor is switchably coupled to the second capacitor; the third capacitor is switchably coupled to the input of the analog-to-digital converter.
  • FIG. 1 shows an example of an electronic device
  • FIG. 2 shows an illustrative embodiment of an electronic device
  • FIG. 3 shows another illustrative embodiment of an electronic device
  • FIG. 4 shows an illustrative embodiment of a position capturing device
  • FIG. 5 shows an illustrative embodiment of a 5-field two-dimensional sensor
  • FIG. 6 shows an illustrative embodiment of filtering of partial sum values
  • FIG. 7 shows an illustrative embodiment of a scan loop for a 5-field two-dimensional sensor
  • FIG. 8 shows an illustrative embodiment of a 6-field two-dimensional sensor
  • FIG. 9 shows an illustrative embodiment of a scan loop for a 6-field two-dimensional sensor
  • FIG. 10 shows an illustrative embodiment of a 9-field two-dimensional sensor
  • FIG. 11 shows an illustrative embodiment of a scan loop for a 9-field two-dimensional sensor.
  • FIG. 1 shows an example of an electronic device 100 .
  • the electronic device 100 comprises a first capacitor (sense capacitor) 108 , a second capacitor (sample-and-hold capacitor) 110 , and an analog-to-digital converter (ADC) 104 .
  • the first capacitor 108 and the second capacitor 110 are switchably coupled to each other (i.e. they are coupled to each other through a controllable switch 116 ).
  • the first capacitor 108 is switchably coupled to an input of the analog-to-digital converter 104 (i.e., coupled through the controllable switch 116 ).
  • the second capacitor 110 is coupled to the input of the analog-to-digital converter 104 .
  • the electronic device 100 may receive a supply voltage through a voltage input 102 , and detect a touch event by measuring a change of the capacitance on the first capacitor (sense capacitor) 108 .
  • capacitor Chold 110 may be charged to a supply voltage V DD received on the voltage input 102 . Then, switch Sadc 112 may be opened and the voltage level V DD may be held on capacitor Chold 110 .
  • switch Sb 114 may be closed, which causes capacitor Csense 108 to discharge to zero. When capacitor Csense 108 is completely discharged switch Sb 114 may be opened. Then, switch Sadc 116 may be closed, so that charge sharing among capacitor Chold 110 and capacitor Csense 108 occurs. The resulting voltage at the input of the ADC 104 is indicative of the capacitance on the capacitor Csense 108 .
  • switch Sadc 116 may be opened and the voltage held on capacitor Chold 110 may now be converted into a digital representation (Dig Out) by means of the ADC 104 .
  • the capacitance on the capacitor Csense 108 may change under the influence of an external object, e.g. a human finger.
  • the voltage at the input of the ADC 104 and its digital representation (Dig Out) changes; this change can be used to detect the presence of the external object.
  • the sense capacitor 108 may correspond to a certain position in an array of sensing elements (sense capacitors), and if the voltage at the input of the ADC 104 and its digital representation (Dig Out) changes, it is concluded that a touch event takes place at this position (this process is referred to as position capturing herein). Since the capacitor Csense 108 is used to sense the presence of, for example, the human finger, it may be referred to as a sense capacitor. Table 1 shows an example of a switching sequence of the electronic device 100 .
  • the electronic device 100 shown in FIG. 1 may have several disadvantages, for example a high power consumption and/or low sensitivity. Furthermore, it may only be applied to single-channel touch sensors. Furthermore, its application may be limited by the size of the sample-and-hold capacitor Chold 110 , which may not be changed. Therefore, the electronic device 100 may not be able to support all sampling schemes. For instance, the electronic device 100 may not be able to support the sampling method presented in the European patent EP 2 667 156 B1, titled “Capacitive position sensor system”. The presently disclosed device and method may overcome at least some of these shortcomings.
  • an electronic device for use in a touch-based user interface comprising a first capacitor, a second capacitor, a third capacitor, and an analog-to-digital converter, wherein: the first capacitor and the second capacitor are switchably coupled to each other; the first capacitor is switchably coupled to an input of the analog-to-digital converter; the second capacitor is coupled to the input of the analog-to-digital converter; the third capacitor is coupled to the first capacitor; the third capacitor is switchably coupled to the second capacitor; the third capacitor is switchably coupled to the input of the analog-to-digital converter.
  • the third capacitor may be used to keep a voltage across the second capacitor within an optimal conversion range of the analog-to-digital converter. This, in turn, may enable a fast and accurate touch position capturing and calculation, thereby reducing the power consumption of sensing systems that comprise the presently disclosed electronic device.
  • FIG. 2 shows an illustrative embodiment of an electronic device 200 .
  • the electronic device 200 comprises a first capacitor (sense capacitor) 108 , a second capacitor (sample-and-hold capacitor) 110 , a third capacitor 202 , and an analog-to-digital converter (ADC) 104 .
  • the first capacitor 108 and the second capacitor 110 are switchably coupled to each other (i.e. they are coupled to each other through a controllable switch 116 ).
  • the first capacitor 108 is switchably coupled to an input of the analog-to-digital converter 104 (i.e., coupled through the controllable switch 116 ).
  • the second capacitor 110 is coupled to the input of the analog-to-digital converter 104 .
  • the third capacitor 202 is coupled to the first capacitor 108 . Furthermore, the third capacitor 202 is switchably coupled to the second capacitor 110 (i.e., coupled through the controllable switch 116 ). Furthermore, the third capacitor 202 is switchably coupled to the input of the analog-to-digital converter 104 (i.e., coupled through the controllable switch 116 ). In operation, the electronic device 200 may receive a supply voltage through a voltage input 102 , and detect a touch event by measuring a change of the capacitance on the first capacitor (sense capacitor) 108 . As mentioned above, the third capacitor 202 may keep a voltage across the second capacitor 110 within an optimal conversion range of the analog-to-digital converter 104 .
  • capacitors Cshare 202 and Chold 110 may be charged to a supply voltage V DD while Csense 108 may be discharged. Discharging of Csense 108 as well as charging Cshare 202 and Chold 110 may be stopped by opening switches Sa 112 and Sb 114 .
  • switch Sc 204 When closing switch Sc 204 , charge sharing among Chold 110 and Csense 108 may occur. The resulting voltage at the input of the ADC 104 is indicative of the capacitance on capacitor Csense 108 .
  • Switch Sadc 116 may be opened and thus the ADC input voltage may be held on Chold 110 for conversion into a digital representation by means of the ADC 104 .
  • the capacitor Cshare 202 may comprise all parasitic capacitances Cypar, for instance the diffusion capacitances of switch Sa 112 , wiring capacitances and track-to-bottom capacitances of the sensor capacitors attached to the y-node.
  • the capacitor Cshare 202 is configured such that the voltage across Chold 110 stays within an optimal conversion range of the ADC 104 .
  • the third capacitor i.e., capacitor Cshare 202
  • capacitor Cshare 202 is implemented as a printed circuit board (PCB) capacitor. More specifically, capacitor Cshare 202 may be implemented as a PCB capacitor made from neighboring tracks, in order to avoid placement of an additional component. Table 2 shows an example of a switching sequence of the electronic device 200 .
  • FIG. 3 shows an illustrative embodiment of an electronic device 300 .
  • the electronic device 200 comprises a set of first capacitors (sense capacitors) 310 , 312 , 314 , a second capacitor (sample-and-hold capacitor) 110 , a third capacitor 202 , and an analog-to-digital converter (ADC) 104 .
  • the first capacitors 310 , 312 , 314 and the second capacitor 110 are switchably coupled to each other (i.e. they are coupled to each other through a controllable switch 116 ).
  • the first capacitors 310 , 312 , 314 are switchably coupled to an input of the analog-to-digital converter 104 (i.e., coupled through the controllable switch 116 ).
  • the second capacitor 110 is coupled to the input of the analog-to-digital converter 104 .
  • the third capacitor 202 is coupled to the first capacitors 310 , 312 , 314 .
  • the third capacitor 202 is switchably coupled to the second capacitor 110 (i.e., coupled through the controllable switch 116 ).
  • the third capacitor 202 is switchably coupled to the input of the analog-to-digital converter 104 (i.e., coupled through the controllable switch 116 ).
  • the electronic device 200 may receive a supply voltage through a voltage input 102 , and detect a touch event by measuring a change of the capacitance on the first capacitors (sense capacitors) 310 , 312 , 314 .
  • the third capacitor 202 may keep a voltage across the second capacitor 110 within an optimal conversion range of the analog-to-digital converter 104 .
  • the electronic device 300 comprises a set of first capacitors (sense capacitors). In this way, multi-channel touch sensors may be supported as well.
  • general-purpose input/output pins GPIOs 304 , 306 , 308 may be used for activating the sense capacitors Csense_ 1 310 , Csense_ 2 312 , Csense_ 3 314 .
  • These GPIOs 304 , 306 , 308 may be controlled by a computer program such that a capacitance measurement method may be facilitated.
  • At least two of the sense capacitors Csense_ 1 310 , Csense_ 2 312 , Csense_ 3 314 may be activated simultaneously by controlling the GPIOs as indicated in Table 3.
  • the activated sensor capacitors may be connected to a supply voltage V DD by means of the related GPIOx.
  • Switch Sadc 116 may be closed so as to charge Chold 110 and the parallel Cshare 202 to V DD , which may be provided by GPIOy 302 set to a high-level output.
  • the measurement may start by setting GPIOy 302 to tri-state.
  • the activated sense capacitors are connected to ground by setting GPIOx to a low-level output, charge sharing between the respective sense capacitor and Chold 110 may occur.
  • Once the voltage across Chold 110 has settled analog-to-digital conversion may be executed by the ADC 104 .
  • the electronic device 300 is configured to derive individual capacitances on the sense capacitors Csense_ 1 310 , Csense_ 2 312 , Csense_ 3 314 , from partial sum values.
  • the partial sum values are obtained by measuring and adding capacitances on subsets of the set of sense capacitors Csense_ 1 310 , Csense_ 2 312 , Csense_ 3 314 .
  • Table 4 shows an example of this principle. In particular, it shows how individual capacitances on the three sense capacitors shown in FIG. 3 are derived from partial sum values ( ⁇ 1 , ⁇ 2 , ⁇ 3 ).
  • the partial sum values are obtained by measuring capacitances on subsets of the set of sense capacitors.
  • the capacitance on two sense capacitors (Csense_ 2 312 , Csense_ 3 314 ) is measured: this does not mean that the individual capacitances on these two sense capacitors is measured, but that a single capacitance measurement is performed on both of them (i.e., a combined capacitance).
  • the capacitances on other subsets of the set of sense capacitors are measured in the second and third step.
  • the individual capacitances on the three capacitors (Csense_ 2 312 , Csense_ 3 314 ) are derived from the partial sum values.
  • two sensing capacitors may be evaluated in every scan cycle.
  • the electronic device 300 is configured to measure capacitances on mutually different subsets of the set of sense capacitors Csense_ 1 310 , Csense_ 2 312 . Csense_ 3 314 .
  • a microcontroller may be used that does not have a sample-and-hold stage preceding the analog-to-digital converter.
  • switch Sadc is kept closed during all steps and capacitor Cshare is used as sample-and-hold capacitor as shown in Table 5.
  • FIG. 4 shows an illustrative embodiment of a position capturing device 400 .
  • the device 400 comprises a microcontroller 402 that may be configured to execute a computer program 408 stored in a memory 404 .
  • the microcontroller 402 also comprises general-purpose input/output pins 302 , 304 , 306 , 308 , an analog-to-digital converter 104 , a central processing unit 406 , sense capacitors Csense_ 1 , Csense_ 2 , Csense_ 3 , and capacitor Cshare.
  • the computer program 408 may request, when executed by the processing unit 406 , positions of touch events on a sensor (i.e., a touch-based user interface).
  • the computer program 408 may invoke a position acquisition function 410 .
  • the position acquisition function 410 may in turn invoke a position filtering function 412 .
  • the position filtering function 412 may invoke an outer FIR-loop 414 , which finally may invoke an inner touch loop 416 .
  • the inner touch loop 416 may comprise processing steps as shown in Table 5.
  • FIG. 5 shows an illustrative embodiment of a 5-field two-dimensional sensor.
  • a 5-field two-dimensional sensor layout 500 is shown on the left side.
  • weights 502 have been assigned to each sensing element.
  • This sensor layout has been described in the European patent application EP 3 035 173 A1, titled “User interface unit, electronic device and manufacturing method”, which is incorporated herein by reference.
  • this 5-field two-dimensional sensor may be implemented using an electronic device of the kind set forth.
  • the sensor may be implemented by an arrangement similar to that shown in FIG. 3 , comprising five sense capacitors instead of three.
  • the evaluation of the five sense capacitors is illustrated in Table 6. After five evaluations of different subsets of the sense capacitors the capacitances of each individual sense capacitor may be obtained by means of a calculation. In a consecutive step the x- and y-position of the touch event may be calculated. In a following step the x- and y-positions may be low-pass filtered in order to remove position noise.
  • the position calculation method may be improved so as achieve higher position sample rates.
  • the x- and y-positions may be calculated directly from the sum samples ⁇ 1 to ⁇ n in case of an n-field sensor.
  • the x- and y-positions of a finger on a 5-field sensor may be directly obtained from weighted filter components ⁇ 1 to ⁇ 5 as shown below:
  • the weighted sums may be regrouped, yielding the two high-pass filter terms ( ⁇ 1 ⁇ 4 ) and ( ⁇ 3 ⁇ 2 ). These high-pass filter terms may remove DC-components from the position components. Only two divisions and a few subtraction, addition and shift operations may be required to obtain one x/y-position from the position components. Thus, in one or more embodiments, the partial sum values may be weighted and the weighted partial sum values may be regrouped. Thereby, hardware savings may be achieved.
  • FIG. 6 shows an illustrative embodiment of filtering 600 of partial sum values.
  • position components may be filtered before calculating an x- and y-position.
  • the position components i.e., partial sum values
  • IIR infinite-impulse-response
  • FIG. 6 The advantage of an IIR filter is that it may be interleaved with the capacitance measuring processing steps in such a way that a filtered x/y-position is available after capturing all partial sums ⁇ 1 to ⁇ n .
  • the filter coefficient a may be chosen as 0 ⁇ a ⁇ 1.
  • the filter coefficient a should be less than 1 but not smaller than 0; a filter coefficient of 0 switches the filter off. The larger a becomes the longer the integration period will be (the lower the filter cut-off frequency will be).
  • FIG. 7 shows an illustrative embodiment of a scan loop for a 5-field two-dimensional sensor.
  • This scan loop 700 performs the following functions: direct FIR-filtering of the measured capacitance values, IIR-filtering of the position components (sum and partial sums), high-pass filtering of partial sums by creation of sample differences, and position calculation from IIR-filtered position components.
  • the scan loop 700 may start with setting the feedback gain of the IIR filters by multiplying the accumulators (Accu 1 , Accu 2 , Accu 3 ) by the filter coefficient a. Subsequently all partial sum samples are captured and immediately added to the required accumulators. When all partial sum samples have been captured the x- and y-positions are calculated from the accumulator contents.
  • no outer control loop may be required beyond the processing steps shown in FIG. 7 .
  • FIG. 8 shows an illustrative embodiment of a 6-field two-dimensional sensor.
  • a 6-field two-dimensional sensor layout 800 is shown on the left side.
  • weights 802 have been assigned to each sensing element.
  • this 6-field two-dimensional sensor may be implemented using an electronic device of the kind set forth.
  • the sensor may be implemented by an arrangement similar to that shown in FIG. 3 , comprising six sense capacitors instead of three. The evaluation of the six sense capacitors is illustrated in Table 7.
  • the calculation of the x- and y-positions may be performed as follows.
  • FIG. 9 shows an illustrative embodiment of a scan loop 900 for a 6-field two-dimensional sensor. Again, three position components may be required to calculate the x/y-position. The processing steps that may be required to obtain a filtered x/y-position from a 6-field sensor, organized as two rows of 3 sensing elements, are shown FIG. 9 . In total three accumulators may be used for capturing the partial sums.
  • FIG. 10 shows an illustrative embodiment of a 9-field two-dimensional sensor.
  • a 9-field two-dimensional sensor layout 1000 is shown on the left side.
  • the same sensor is shown, in which weights 1002 have been assigned to each sensing element.
  • this 9-field two-dimensional sensor may be implemented using an electronic device of the kind set forth.
  • the sensor may be implemented by an arrangement similar to that shown in FIG. 3 , comprising nine sense capacitors instead of three.
  • the evaluation of the nine sense capacitors is illustrated in Table 8. More specifically, the left side of FIG. 10 shows the position of nine individual sensing elements (corresponding to sense capacitors) while the right side of FIG. 10 shows the x- and y-position weights assigned to each individual sensing element, as may be required to perform a center-of-gravity calculation.
  • the scanning steps and the resulting partial sums are shown in Table 8.
  • the x/y-position may be obtained directly from the partial sums ⁇ 1 to ⁇ 9 as shown below:
  • Pos X 8*( ⁇ 1 ⁇ 3 + ⁇ 4 ⁇ 6 + ⁇ 7 ⁇ 9 )/ ⁇
  • Pos X 8*(( ⁇ 1 ⁇ 9 )+( ⁇ 7 ⁇ 3 )+( ⁇ 4 ⁇ 6 ))/ ⁇
  • Pos y 8*( ⁇ 1 ⁇ 2 ⁇ 3 + ⁇ 7 + ⁇ 8 + ⁇ 9 )/ ⁇
  • Pos y 8*( ⁇ ( ⁇ 1 ⁇ 9 )+( ⁇ 7 ⁇ 3 )+( ⁇ 8 ⁇ 2 ))/ ⁇
  • the IIR-filtered partial differences ( ⁇ 1 ′ ⁇ 9 ′), ( ⁇ 7 ′ ⁇ 3 ′), ( ⁇ 4 ′ ⁇ 6 ′), and ( ⁇ 8 ′ ⁇ 2 ′) as well as the filtered sum ⁇ ′ are required to calculate the filtered x/y-position.
  • the partial differences may remove DC-values from the position components.
  • FIG. 11 shows an illustrative embodiment of a scan loop for a 9-field two-dimensional sensor. This embodiment provides an example of a combined FIR/IIR filter-acquisition-loop for a 9-field sensor.
  • ⁇ x ⁇ (2 n )*[ Wx 1 * ⁇ 1 +Wx 2 * ⁇ 2 + . . . +Wx n * ⁇ n ]
  • Wx n and Wy n are the position weight factors for weighted averaging; Wx i /Wy i practically define the position of the center of sensor i in a reference plane.
  • the presently disclosed electronic device may be used to advantage in a smart card.
  • a typical application of a five-sensor structure is a keypad or PIN pad for smart cards, e.g. for authentication purposes in banking and payment applications.
  • the identified touch position may be communicated to a secure element embedded in the smart card, for personal identification number (PIN) decoding and PIN matching.
  • PIN personal identification number
  • Another implementation of the touch processing sequence may be the physical integration as a hardware component into a microcontroller, because the simplicity of the sequence of processing steps may support an efficient implementation with an economic gate-count.
  • a 3 ⁇ 3 sensor structure may also be applied as a user input interface for a wide range of consumer devices with touchpad sizes of up to 60 ⁇ 60 mm.
  • any reference sign placed between parentheses shall not be construed as limiting the claim.
  • the word “comprise(s)” or “comprising” does not exclude the presence of elements or steps other than those listed in a claim.
  • the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.
  • Measures recited in the claims may be implemented by means of hardware comprising several distinct elements and/or by means of a suitably programmed processor. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

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